The present invention relates to solid freeform fabrication and, more particularly, selective laser sintering, using certain thermoplastic polyurethanes.
Solid Freeform Fabrication (SFF) is a technology enabling fabrication of arbitrarily shaped structures directly from computer data via additive formation steps. The basic operation of any SFF system consists of slicing a three-dimensional computer model into thin cross sections, translating the result into two-dimensional position data and feeding the data to control equipment which fabricates a three-dimensional structure in a layer-wise manner.
Solid freeform fabrication entails many different approaches to the method of fabrication, including three-dimensional printing, electron beam melting, stereolithography, selective laser sintering, laminated object manufacturing, fused deposition modeling and others.
In three-dimensional printing processes, for example, a building material is dispensed from a dispensing head having a set of nozzles to deposit layers on a supporting structure. Depending on the building material, the layers may then be cured or solidified using a suitable device. The building material may include modeling material, which forms the object, and support material, which supports the object as it is being built.
Solid freeform fabrication is typically used in design-related fields where it is used for visualization, demonstration and mechanical prototyping. Thus, SFF facilitates rapid fabrication of functioning prototypes with minimal investment in tooling and labor. Such rapid prototyping shortens the product development cycle and improves the design process by providing rapid and effective feedback to the designer. SFF can also be used for rapid fabrication of non-functional parts, e.g., for the purpose of assessing various aspects of a design such as aesthetics, fit, assembly and the like. Additionally, SFF techniques have been proven to be useful in the fields of medicine, where expected outcomes are modeled prior to performing procedures. It is recognized that many other areas can benefit from rapid prototyping technology, including, without limitation, the fields of architecture, dentistry and plastic surgery where the visualization of a particular design and/or function is useful.
There is growing interest in this form of fabrication. Many materials have been considered for use in such systems and methods using the same, however, thermoplastic polyurethanes have proven difficult to utilize in these systems and methods. This is due at least in part to the difficulty in processing the TPU into the proper particle size distribution and making sure the physical properties of the TPU are well suited for selective laser sintering processing. The low crystallization rate of TPU can also make it difficult to maintain tolerances when laying down the melt stream onto the parts being built. Further, the broad melt range for TPU materials can make viscosity control somewhat challenging and there may be fuming or off gassing issues with using many TPU materials.
Given the attractive combination of properties thermoplastic polyurethanes may offer, and the wide variety of articles made using more conventional means of fabrication, there is a growing need to identify and/or develop thermoplastic polyurethanes well suited for solid freeform fabrication, and particularly selective laser sintering.